Add stamina reduce multiplier parameter

[muertoof]

At the moment, plugin devs can change players movement speed and jump height via pluginSpeedMultiplier and pluginJumpMultiplier. It would be cool to add a parameter that affect players stamina reduce, e.g: pluginStaminaMultiplier. And even better, separate it into: pluginSprintStaminaMultiplier and pluginJumpStaminaMultiplier.

Adding this option will allow plugin devs to more flexibly control player's movement and add new mechanics that affect it.